1. Field of the Invention
This invention relates to replaceable nozzles for rock bits utilizing drilling mud to remove detritus from an earthen formation borehole.
More particularly, this invention relates to mini-extended nozzles that are fabricated from a composite of materials to both resist erosion of the nozzle from the drilling mud and to prevent nozzle breakage caused by contact of the nozzle tip with obstructions in the formation borehole during a drilling operation.
2. Background
Extended nozzles of varying length have been used in petroleum bits for several years. Obviously, the longer the nozzle is the more vulnerable it is to breakage since the extended end is normally unsupported.
Moreover, composite hydraulic nozzles have been developed and patented by others in the rock bit industry.
U.S. Pat. No. 3,111,179 teaches the fabrication of a jet nozzle of composite material. The nozzle consists of a thin walled inner shell of tungsten carbide material that is bonded to a plastic body. The body serves to back up and support the erosion resistant but brittle tungsten carbide inner shell. The patent further teaches that, should the nozzle be ejected from the rock bit, it would easily be ground up by the cutter cones and removed from the borehole along with the formation cuttings since the hard shell is brittle and the back up material is relatively soft.
This nozzle could not be readily extended since the back up material taught would not be strong enough to support the thin inner shell.
U.S. Pat. No. 4,392,534 discloses a composite nozzle for earth boring bits. The nozzle consists of a ceramic body encased within a thin metal cylindrical shell and a metal reinforcing end plate at the nozzle exit plane. This nozzle also is disadvantaged in that it lacks sufficient support to withstand an exposure to the rock formation should the nozzle be extended beyond the bit body.
U.S. Pat. Nos. 4,665,999; 687,067; and 4,711,311 assigned to the same assignee as the present invention all reflect rock bit nozzle designs and are incorporated herein by reference.
The '999 reference teaches the use of standard nozzles mounted within extended portions of the bit body. The '067 patent is a mini-extended nozzle fabricated entirely of tungsten carbide and the '311 reference is a means to retain a nozzle body within a nozzle receptacle formed in the bit body.
The mini-extended nozzle taught by the '067 reference, while its performance is outstanding, is vulnerable to breakage should the extended end of the nozzle encounter an obstruction downhole. Should the nozzle break, nozzle washout is a possible consequence.
The present invention overcomes the inadequacies of the foregoing prior art by providing a composite mini-extended nozzle that will withstand the harsh environment downhole. A means is also provided to further protect the extended portion of the nozzle body to insure the integrity of the nozzle.
An additional means is disclosed to vary the length of the nozzle support body to further vary the distance of the exit plane of the mini-extended nozzle with respect to a borehole bottom.